Or, enter specific values in the width and height boxes.

Drag the handles to resize the viewport to whatever dimensions you need. Use Remote Debugging to view, change, debug, and profile a page's code from your laptop or desktop while it actually runs on a mobile device. When in doubt, your best bet is to actually run your page on a mobile device. There are some aspects of mobile devices that DevTools will never be able to simulate. You simulate the mobile user experience from your laptop or desktop. With Device Mode you don't actually run your code on a mobile device.

Think of Device Mode as a first-order approximation of how your page looks and feels on a mobile device. Device Mode is the name for the loose collection of features in Chrome DevTools that help you simulate mobile devices.